Because fuel cells are sized based on their high-power requirement, improvements in the high-power capability (W/cm²) can directly be translated to reduced active area and thus reduced cost. For proton-exchange-membrane (PEM) fuel cells, state-of-the-art PtCo catalysts on several different carbon supports have exhibited impressive and similar kinetic (low-current-density) activity. However, it is now becoming clear that the carbon-support selection can be important in determining their high-power performance. At beginning of life, we have recently observed that active nanoparticles reside predominantly within some porous carbon support particles and are apparently shielded from direct contact with the solid ionomer electrolyte as shown in the second illustration in Figure 1. This raises questions involving O₂ and proton transport mechanisms and possible rate limitations within these primary carbon particles.

In this work, we will present a mathematical model that includes the cathode-reactant-transport processes within a porous carbon support, allowing estimation of Pt utilization as a function of material parameters and operating conditions. We will also report recent experimental work that we are bringing alongside the model in attempts to validate and develop it further. Finally, we will discuss the implications for optimizing the support and the active-material location within it.

References

1) E. Padgett et al., Proceeding of Microscopy & Microanalysis 2015 Volume 21, Issue S3, August 2015, pp. 799-800.

This work was partially supported by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy under grant DE-EE0007271.